The impact of angiogenesis is well known for the growth and viability of solid tumors. Fewer studies have been published relating angiogenesis to clinical or pathological parameters in hematological malignancies. In this report, we have estimated the bone marrow microvessel density (MVD) before and after conventional-dose or high-dose chemotherapy with autologous stem cell transplantation. Immunohistochemical CD34-stained paraffin-embedded bone marrow biopsies of 21 patients with stage III multiple myeloma were studied. Microvessels were counted at 400x magnification, and the mean number of vessels per area in each sample was noted as the MVD. The median MVD of all patients was 53.1 vessels/mm2 (range 15.5-174.7 vessels/mm2) before treatment and 29.3 vessels/mm2 (range 0-221.1 vessels/mm2) after chemotherapy. The post-treatment MVD in the two groups of patients with and without remission was significantly different (p=0.001), whereas the pretreatment MVD was not. Responders but not nonresponders showed a significant decrease of MVD after therapy in comparison to their pretreatment levels. The progression-free survival in patients who achieved a reduction in MVD after chemotherapy was significantly longer than in patients without a decrease in MVD (P=0.006). Furthermore, we compared the MVD of patients after achievement of a remission to MVD of 15 untreated stage I myeloma patients. The MVD of patients in remission was not statistically different from the MVD in stage I myeloma. These results underscore the impact of angiogenesis in myeloma and give the first report that effective chemotherapy is accompanied by a significant decrease in bone marrow angiogenesis in this disease.